Conductivity measurement sensors are well known in the art and are used to measure the conductivity of a fluid, such as a liquid or a dispersion of solids suspended in a liquid. Conductivity sensors are often used to investigate the properties of electrolytes in solution, such as the degree of disassociation, the formation of chemical complexes, and hydrolysis. The conductivity of a fluid may also be used to measure a wide variety of other parameters, such as the amount of contaminants in drinking water and a measure of chemical concentrations in industrial process streams. Applications such as these involve the determination of conductivities in many different physical environments.
Toroidal conductivity sensors generally include two toroidal coils. The first coil is electrically excited by an alternating current source to generate a changing magnetic field. The changing magnetic field induces an electrical current in the liquid. In electrolytic solutions, the mechanism of electrical current transfer is dependent on ions. The magnitude of the induced current is indicative of the conductivity of the liquid. The second coil detects the magnitude of the induced current. Typically, toroidal conductivity sensors are best suited for use in processes where conventional conductivity sensors, such as those with electrodes exposed to the measured solution, would corrode or become foul.
One example of a toroidal conductivity sensor is sold under the trade designation Model 242 available from the Rosemount Analytical, Incorporated Division of Emerson Process, which division is located in Irvine, Calif. The Model 242 sensor is designed to be installed easily into process piping between mounting flanges. As a flow-through conductivity sensor, the Model 242 is not sensitive to flow rate or direction and it does not obstruct the flow of process fluid. Typically, a flow-through conductivity sensor, such as the Model 242 is electrically coupled to a compatible instrument such as instrument models 54eC, 1055, 3081T, 4081T and 5081T, all of which are available from the Rosemount Analytical, Incorporated Division of Emerson Process.
Toroidal conductivity sensors of the prior art have generally performed well. One limitation of such sensors, however, has been that when sensors are offered for different pipe sizes, different sized toroids must be manufactured to accommodate the various pipe sizes. Once a company offers three or four pipe sizes as well as toroids having different winding counts for each pipe size, the sheer number of different toroids that must be manufactured grows quickly. This tends to drive up manufacturing costs since the individual lots of toroids are relatively smaller. Providing a toroidal-type conductivity sensor that could use standardized toroids would allow manufacturing of such toroids to be done on a much larger scale and thus the component cost of the toroid reduced thereby also reducing costs of the final unit.